The present invention relates generally to temperature control apparatus for liquids and more specifically to temperature control apparatus for use in photographic processors.
Photographic processors, of the type used to develop conventional photographic film or paper, utilize a plurality of processing fluids which must be maintained at precise temperatures. A typical photographic paper processor includes, for example, six discrete tanks of processing fluids including: a developing fluid, a bleaching fluid, and four separate tanks of stabilizing fluids. The temperature of each of these fluids must be maintained, within a certain tolerance, at a precise setting. Further, the fluids can't be intermixed, so it is necessary to separately maintain the temperature of each fluid in each tank.
The maintenance of the individual fluid temperatures is accomplished, in some modern photographic processors, by providing a separate temperature control system for each tank of fluid. Each temperature control system includes its own temperature sensor situated in the fluid, its own heating element also situated in the fluid, and its own control electronics connected to both the temperature sensor and the heater. Each temperature control system operates by monitoring the temperature of the sensor with the control electronics, and using the control electronics to actuate the heating element as required. While providing extremely precise temperature control, the use of such individual temperature control systems is expensive. Further, they require a substantial quantity of complex electronic parts, adding to the complexity, bulk, and difficulty in maintaining the photographic processors employing them.
It would thus be desirable to provide a photographic processor including temperature control apparatus which is capable of maintaining fluid temperatures within required tolerances using a minimal amount of relatively simple and economical hardware.